The general goal of this work is to determine the kinetic mechanisms of sodidum dependent amino acid transport in animal cells. This mechanisms of sodium dependent amino acid transport in animal cells. This goal is important because sodium dependent systems are the principle means for accumulatin and regulation of amino acids by cells yet little is understood about them. This project will focus on the kinetics of taurine efflux from internally dialyzed giant axons of Myxicola infundibulum. The specific aims are: 1. Define the taurine efflux as a function of the internal and external concentrations of sodium and taurine. 2. Define the taurine efflux as a function of membrane potential. 3. Measure the sodium-taurine flux coupling directly. 4. Define the rold of ATP in taurine transport.